Gas optimizations - Remove isMarket from RCMarket

[code423n4]

Handle

a_delamo

Vulnerability details

Impact

RCMarket contains the constant variable isMarket to indicate it is a Market bool public constant override isMarket = true;.
This is after used in RCFactory

function changeMarketApproval(address _market) external onlyGovernors {
        require(_market != address(0));
        // check it's an RC contract
        IRCMarket _marketToApprove = IRCMarket(_market);
        assert(_marketToApprove.isMarket());
        isMarketApproved[_market] = !isMarketApproved[_market];
        emit LogMarketApproved(_market, isMarketApproved[_market]);
    }

Why not use mappingOfMarkets to verify the address is a Market? This would reduce the state space used.

[Splidge]

That certainly would be easier 👍

[Splidge]

In implementing this I discovered the problem.
The check isMarket() is mainly used when we deploy a new reference market contract. This checks that it is a market but doesn't add it to the mappingOfMarkets because it's not actually an active market.
I've changed changeMarketApproval to use the mapping in this commit but I'm going to leave the constant isMarket in the market mainly for the check in setReferenceContractAddress()